Post-column addition as a method of controlling triacylglycerol response coefficient of an evaporative light scattering detector in liquid chromatography–evaporative light-scattering detection

The non-linear response is generally the main limitation to the general quantitative use of evaporative light-scattering detection (ELSD). In the particular case of triacylglycerol (TG) analysis, we present a preliminary paper dealing with the use of post-column additives as a means of monitoring the response of such a detector. As TG can form molecular association complexes (ligand–ligate associations) with either cholesterol, urea or silver nitrate, we report the influence of the concentration of each of these chemical compounds in the liquid phase directed towards the ELSD system. The results show that the response coefficient b of the calibration curve either decreases from 1.25–1.30 to 0.51 or increases from 1.25–1.30 to 1.78 according to the nature and concentration of post-column additive. The use of cholesterol as additive, at a discrete concentration, may lead to a linear response curve (b=1), i.e. to the direct proportionality of ELSD response versus the TG concentration, making quantitative analysis of such solutes easier. On the other hand, to improve sensitivity, the addition of silver nitrate may be chosen for an increase in b value.